6.2 The blood system Essential idea: The blood system continuously transports substances to cells and simultaneously collects waste products.

Understandings: Arteries convey blood at high pressure from the ventricles to the tissues of the body. Arteries have muscle cells and elastic fibres in their walls. The muscle and elastic fibres assist in maintaining blood pressure between pump cycles. Blood flows through tissues in capillaries. Capillaries have permeable walls that allow exchange of materials between cells in the tissue and the blood inthe capillary. Veins collect blood at low pressure from the tissues of the body and return it to the atria of the heart. Valves in veins and the heart ensure circulation of blood by preventing backflow. There is a separate circulation for the lungs. The heart beat is initiated by a group of specialized muscle cells in the right atrium called the sinoatrial node. The sinoatrial node acts as a pacemaker. The sinoatrial node sends out an electrical signal that stimulates contraction as it is propagated through the walls of the atria and then the walls of the ventricles. The heart rate can be increased or decreased by impulses brought to the heart through two nerves from the medulla of the brain. Epinephrine increases the heart rate to prepare for vigorous physical activity.

Applications and skills: Application: William Harvey’s discovery of the circulation of the blood with the heart acting as the pump. Application: Pressure changes in the left atrium, left ventricle and aorta during the cardiac cycle. Application: Causes and consequences of occlusion of the coronary arteries. Skill: Identification of blood vessels as arteries, capillaries or veins from the structure of their walls. Skill: Recognition of the chambers and valves of the heart and the blood vessels connected to it in dissected hearts or in diagrams of heart structure.

Warm Up How does blood move around your body? What path does it follow? TODAY’S FOCUS – HEART AND BLOOD VESSELS What are the major structures of the circulatory system?

body Aorta lungs Pulmonary Artery Vena Cava Pulmonary Vein Right Atrium Left Atrium Right Ventricle Left Ventricle blood flow

beating heart pulmonary artery (to left lung) aorta superior vena cava left atrium pulmonary artery (to left lung) semilunar valves pulmonary veins (from left lung) atrioventricular valve left ventricle thicker muscle of left ventricle descending aorta (to lower body) right ventricle inferior vena cava superior vena cava pulmonary artery (to right lung) pulmonary veins (from right lung) right atrium beating heart Figure taken from Biology, Life on Earth 10th Ed. Pearson

How Does The Vertebrate Heart Work? The cardiac cycle Oxygenated blood is pumped to the body Deoxygenated blood is pumped to the lungs Blood fills the atria and begins to flow passively into the ventricles Deoxygenated blood from the body enters the right ventricle Oxygenated blood from the lungs enters the left ventricle Atria contract, forcing blood into the ventricles Then the ventricles contract, forcing blood through the arteries to the lungs and the rest of the body The cycle ends as the heart relaxes Fig. 20-4

How Does The Vertebrate Heart Work? The heart’s pacemaker and its connections The sinoatrial node electrical signal starts the atrial contraction Unexcitable tissue separates the atria and ventricles AV node The signal spreads, causing the atria to contract excitable fibers The atrioventricular node transmits the signal to the ventricles with a slight delay The signal travels to the base of the ventricles Excitable fibers transmit the signals to ventricular cardiac muscle, causing contraction from the base upwards

lung capillaries atria ventricle body capillaries Figure taken from Biology, Life on Earth 10th Ed. Pearson

Anatomy of Circulatory Systems arteries - vessels that carry blood away from the heart capillaries - smallest blood vessels (microscopic) penetrate tissues extracellular fluid - fluid surrounding capillaries; dissolved substances in the blood are exchanged veins – vessels that move blood back toward the heart

capillary network arteriole venule cross section capillary valve smooth muscle connective tissue artery vein Figure taken from Biology, Life on Earth 10th Ed. Pearson

jugular vein aorta superior vena cava carotid artery lung capillaries pulmonary artery heart kidney femoral vein intestine inferior vena cava liver femoral artery

circulatory systems transport… oxygen from the lungs or gills to the tissues carbon dioxide from the tissues to the lungs or gills nutrients from the digestive system to the tissues waste products & toxins to the liver & kidney for excretion hormones from the glands and organs that produce them to the tissues on which they act